The reaction pathways in the bromination and protodebromination of 3-phenanthrols have been studied.
When 3-phenanthrol (1) was treated with bromine in carbon tetrachloride at 0°C in the presence or the absence of anhydrous sodium carbonate, 4-bromo-3-phenanthrol (2) or 9-bromo-3-phenanthrol (3) was obtained, respectively. In contact with dry hydrogen bromide, (2) was readily isomerized into (3). When this isomerzation reaction of (2) was conducted in the presence of 2-phenanthrol (4), 1-bromo-2-phenanthrol (5) was also obtained.
These facts suggest the following reaction scheme.
(2)+HBr _??_ (1)+Br
2→ (3)+HBr
(4) →→ (5)+HBr
(2) and 2, 4, 9-tribromo-3-phenanthrol (6) were also prepared from (1) and 2, 9-dibromo-3-phenanthrol (7), respectively, by the reaction with N-bromo-
tert-butylamine. When heated with hydrogen bromide, (6) was debrominated to give (7) and free bromine.
The structures of (2) and (6) were determined by converting into respective known compounds.
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